Fourth-root summation of contrast over area:no end in sight when spatially inhomogeneous sensitivity is compensated by a witch's hat

Measurements of area summation for luminance-modulated stimuli are typically confounded by variations in sensitivity across the retina. Recently we conducted a detailed analysis of sensitivity across the visual field (Baldwin et al, 2012) and found it to be well-described by a bilinear “witch’s hat” function: sensitivity declines rapidly over the first 8 cycles or so, more gently thereafter. Here we multiplied luminance-modulated stimuli (4 c/deg gratings and “Swiss cheeses”) by the inverse of the witch’s hat function to compensate for the inhomogeneity. This revealed summation functions that were straight lines (on double log axes) with a slope of -1/4 extending to ≥33 cycles, demonstrating fourth-root summation of contrast over a wider area than has previously been reported for the central retina. Fourth-root summation is typically attributed to probability summation, but recent studies have rejected that interpretation in favour of a noisy energy model that performs local square-law transduction of the signal, adds noise at each location of the target and then sums over signal area. Modelling shows our results to be consistent with a wide field application of such a contrast integrator. We reject a probability summation model, a quadratic model and a matched template model of our results under the assumptions of signal detection theory. We also reject the high threshold theory of contrast detection under the assumption of probability summation over area.

Development of a quality control material for the measurement of 8-oxo-7,8-dihydro-2'-deoxyguanosine, an in vivo marker of oxidative stress, and comparison of results from different laboratories

The measurement of 8-oxo-7,8-dihydro-2'-deoxyguanosine is an increasingly popular marker of in vivo oxidative damage to DNA. A random-sequence 21-mer oligonucleotide 5'-TCA GXC GTA CGT GAT CTC AGT-3' in which X was 8-oxo-guanine (8-oxo-G) was purified and accurate determination of the oxidised base was confirmed by a 32P-end labelling strategy. The lyophilised material was analysed for its absolute content of 8-oxo-dG by several major laboratories in Europe and one in Japan. Most laboratories using HPLC-ECD underestimated, while GC-MS-SIM overestimated the level of the lesion. HPLC-ECD measured the target value with greatest accuracy. The results also suggest that none of the procedures can accurately quantitate levels of 1 in 10(6) 8-oxo-(d)G in DNA.

The Post-Growth Project:how the end of economic growth could bring a fairer and happier society

This book challenges the assumption that it is bad news when the economy doesn’t grow. For decades, it has been widely recognized that there are ecological limits to continuing economic growth and that different ways of living, working and organizing our economies are urgently required. This urgency has increased since the financial crash of 2007–2008, but mainstream economists and politicians are unable to think differently. The authors of this book demonstrate why our economic system demands ecologically unsustainable growth and the pursuit of more ‘stuff’. They believe that what matters is quality, not quantity – a better life based on having fewer material possessions, less production and less work. Such a way of life will emphasize well‑being, community, security and ‘conviviality’. That is, more real wealth. The book will therefore appeal to everyone curious as to how a new post-growth economics can be conceived and enacted. It will be of particular interest to policy makers, politicians, businesspeople, trade unionists, academics, students, journalists and a wide range of people working in the not-for-profit sector. All of the contributors are leading thinkers on green issues and members of the new think-tank Green House.